Method and apparatus for generating reference signals for accurate time-difference of arrival estimation

ABSTRACT

A base station communicates a positioning reference signal (PRS) to wireless communication devices over a downlink in a wireless communication system by encoding a PRS into a first set of transmission resources, encoding other information into a second set of transmission resources, multiplexing the two sets of resources into a subframe such that the first set of resources is multiplexed into at least a portion of a first set of orthogonal frequency division multiplexed (OFDM) symbols based on an identifier associated with the base station and the second set of resources is multiplexed into a second set of OFDM symbols. Upon receiving the subframe, a wireless communication device determines which set of transmission resources contains the PRS based on the identifier associated with the base station that transmitted the subframe and processes the set of resources containing the PRS to estimate timing (e.g., time of arrival) information.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a non-provisional application of co-pendingU.S. Application No. 61/168,189 filed on 9 Apr. 2009, the contents ofwhich are hereby incorporated by reference and from which benefits areclaimed under 35 U.S.C. 119.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to wireless communicationnetworks and, more particularly, to an apparatus and method forcommunicating and processing positioning reference signals in a downlinksubframe based on an identifier associated with a base stationtransmitting the subframe.

BACKGROUND

Wireless communication networks are well known. Some networks arecompletely proprietary, while others are subject to one or morestandards to allow various vendors to manufacture equipment for a commonsystem. One such standards-based network is the Universal MobileTelecommunications System (UMTS). UMTS is standardized by the ThirdGeneration Partnership Project (3GPP), a collaboration between groups oftelecommunications associations to make a globally applicable thirdgeneration (3G) mobile phone system specification within the scope ofthe International Mobile Telecommunications-2000 project of theInternational Telecommunication Union (ITU). Efforts are currentlyunderway to develop an evolved UMTS standard, which is typicallyreferred to as UMTS Long Term Evolution (LTE) or Evolved UMTSTerrestrial Radio Access (E-UTRA).

According to Release 8 of the E-UTRA or LTE standard or specification,downlink communications from a base station (referred to as an “enhancedNode-B” or simply “eNB”) to a wireless communication device (referred toas “user equipment” or “UE”) utilize orthogonal frequency divisionmultiplexing (OFDM). In OFDM, orthogonal subcarriers are modulated witha digital stream, which may include data, control information, or otherinformation, so as to form a set of OFDM symbols. The subcarriers may becontiguous or discontiguous and the downlink data modulation may beperformed using quadrature phase shift-keying (QPSK), 16-ary quadratureamplitude modulation (16QAM), or 64QAM. The OFDM symbols are configuredinto a downlink subframe for transmission from the base station. EachOFDM symbol has a time duration and is associated with a cyclic prefix(CP). A cyclic prefix is essentially a guard period between successiveOFDM symbols in a subframe. According to the E-UTRA specification, anormal cyclic prefix is about five (5) microseconds and an extendedcyclic prefix is 16.67 microseconds.

In contrast to the downlink, uplink communications from the UE to theeNB utilize single-carrier frequency division multiple access (SC-FDMA)according to the E-UTRA standard. In SC-FDMA, block transmission of QAMdata symbols is performed by first discrete Fourier transform(DFT)-spreading (or precoding) followed by subcarrier mapping to aconventional OFDM modulator. The use of DFT precoding allows a moderatecubic metric/peak-to-average power ratio (PAPR) leading to reduced cost,size and power consumption of the UE power amplifier. In accordance withSC-FDMA, each subcarrier used for uplink transmission includesinformation for all the transmitted modulated signals, with the inputdata stream being spread over them. The data transmission in the uplinkis controlled by the eNB, involving transmission of scheduling requests(and scheduling information) sent via downlink control channels.Scheduling grants for uplink transmissions are provided by the eNB onthe downlink and include, among other things, a resource allocation(e.g., a resource block size per one millisecond (ms) interval) and anidentification of the modulation to be used for the uplinktransmissions. With the addition of higher-order modulation and adaptivemodulation and coding (AMC), large spectral efficiency is possible byscheduling users with favorable channel conditions.

E-UTRA systems also facilitate the use of multiple input and multipleoutput (MIMO) antenna systems on the downlink to increase capacity. Asis known, MIMO antenna systems are employed at the eNB through use ofmultiple transmit antennas and at the UE through use of multiple receiveantennas. A UE may rely on a pilot or reference symbol (RS) sent fromthe eNB for channel estimation, subsequent data demodulation, and linkquality measurement for reporting. The link quality measurements forfeedback may include such spatial parameters as rank indicator, or thenumber of data streams sent on the same resources; precoding matrixindex (PMI); and coding parameters, such as a modulation and codingscheme (MCS) or a channel quality indicator (CQI). For example, if a UEdetermines that the link can support a rank greater than one, it mayreport multiple CQI values (e.g., two CQI values when rank=2). Further,the link quality measurements may be reported on a periodic or aperiodicbasis, as instructed by an eNB, in one of the supported feedback modes.The reports may include wideband or subband frequency selectiveinformation of the parameters. The eNB may use the rank information, theCQI, and other parameters, such as uplink quality information, to servethe UE on the uplink and downlink channels.

As is also known, present-day cellular telephones include globalpositioning system (GPS) receivers to assist in locating the devices andtheir owners in the event of an emergency and to comply with E-911mandates from the Federal Communication Commission (FCC). Under mostcircumstances, the phone's GPS receiver can receive signals from theappropriate quantity of GPS satellites and convey that information tothe cellular system's infrastructure for determination of the device'slocation by, for example, a location server coupled to or forming partof the wireless network. However, there are some circumstances underwhich the GPS receiver is ineffective. For example, when a user and hisor her cell phone are located within a building, the GPS receiver maynot be able to receive signals from an appropriate quantity of GPSsatellites to enable the location server to determine the device'sposition. Additionally, wireless devices in private systems are notrequired to meet the FCC E-911 mandates and may not include a GPSreceiver. However, circumstances may arise under which determininglocations of wireless devices operating in such systems may benecessary.

To compensate for the intermittent ineffectiveness of the GPS system andto provide location-determining capabilities in private systems, manywireless systems utilize signaling and include processes through which awireless device's location can be estimated. For example, in manysystems, base stations regularly transmit positioning reference signalsthat are received by the wireless devices and used either to determineinformation based upon which an infrastructure device, such as alocation server, can compute (e.g., via triangulation and/ortrilateration) the wireless device's location or to determine thelocation of the wireless device autonomously (i.e., at the wirelessdevice itself). When a location server is intended to compute thewireless device's location, the wireless device may determine time ofarrival (TOA) or time difference of arrival (TDOA) information uponreceiving the positioning reference signal and communicate the TOA orTDOA to the location server via a serving base station (i.e., a basestation providing wireless communication service to the wirelessdevice). The TOA or TDOA information is typically determined based on aninternal clock of the wireless device as established by the wirelessdevice's local oscillator in accordance with known techniques.

Contribution R1-090353 to the 3GPP Radio Access Network (RAN) WorkingGroup 1 (3GPP RAN1) provides one approach for developing downlinksubframes for use in conveying positioning reference signals to UEs inE-UTRA systems. According to Contribution R1-090353, QPSK symbolscontaining the positioning reference signal are distributed throughoutOFDM symbols that are not allocated to control information such that tworesource elements per resource block per OFDM symbol carry thepositioning reference symbols. FIG. 1 illustrates exemplary downlinksubframes 101, 103 transmitted by eNBs serving cells neighboring thecell in which the UE is currently operating. As illustrated, eachsubframe 101, 103 includes a resource block of twelve subcarriers (sub₀through sub₁₁), each of which is divided into twelve time segments (t₀through t₁₁). Each time segment on a particular subcarrier is a resourceelement 102, 104, which contains a digitally modulated (e.g., QPSK,16QAM or 64 QAM) symbol. A set of resource elements 102, 104 spreadacross all the subcarriers during a particular segment or duration oftime forms an OFDM symbol. A set of OFDM symbols (twelve as illustratedin FIG. 1) forms each subframe 101, 103.

In the illustrated subframes 101, 103, the first two OFDM symbols ofeach subframe 101, 103 include cell-specific reference symbols (denoted“CRS” in the subframes 101, 103) and other control information (denotedas “C” in the subframes 101, 103) and the remaining OFDM symbols containthe positioning reference signal encoded as symbols into two resourceelements 102 of each OFDM symbol. The resource elements 102, 104containing the positioning reference signal are denoted “PRS” in thesubframes 101, 103. The eNBs transmitting the subframes 101, 103 arecontrolled by one or more controllers in an attempt to maintainorthogonality of the arrangement of the positioning reference signalswithin the non-control portions of the subframes 101, 103 by insuringthat the positioning reference signal symbols are multiplexed intonon-overlapping resource elements 102, 104. Notwithstanding such intentto maintain orthogonality in this manner, the proposed subframestructure may cause a loss of orthogonality under certain conditions.For example, when using a normal cyclic prefix (CP) for each OFDM symbolin the exemplary subframes 101, 103, an inter-site distance (ISD) of 1.5kilometers and a channel delay spread of five microseconds can result ina loss of orthogonality between the different eNB transmitters even whenthey transmit on non-overlapping resource elements 102, 104 asillustrated in FIG. 1. The loss of orthogonality results because theoverall delay spread of the downlink channel (i.e., propagation delayplus multipath delay spread) as seen from the UE exceeds the CP lengthfor normal CP (approximately five microseconds) and, therefore, DFTprecoding is non-orthogonal. For the case of an extended CP(approximately 16.67 microseconds) deployment, an ISD of 4.5 km and achannel delay spread of five microseconds can result in loss oforthogonality of subcarrier transmissions.

The various aspects, features and advantages of the disclosure willbecome more fully apparent to those having ordinary skill in the artupon careful consideration of the following Detailed Description thereofwith the accompanying drawings described below.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying figures where like reference numerals refer toidentical or functionally similar elements throughout the separate viewsand which together with the detailed description below are incorporatedin and form part of the specification, serve to further illustratevarious embodiments and to explain various principles and advantages allin accordance with the one or more embodiments of the disclosure.

FIG. 1 is an exemplary downlink subframe for transmitting a positioningreference signal from a base station to a wireless communication devicein accordance with the E-UTRA standard.

FIG. 2 is an electrical block diagram of a wireless communication systemproviding wireless communication service to a wireless communicationdevice in accordance with an exemplary embodiment of the presentinvention.

FIG. 3 illustrates electrical block diagrams of an exemplary basestation usable in the wireless communication system of FIG. 2 and awireless communication device, in accordance with an exemplaryembodiment of the present invention.

FIG. 4 is a logic flow diagram of steps executed by a base station togenerate a downlink subframe for transmission of a positioning referencesignal to a wireless communication device, in accordance with anexemplary embodiment of the present invention.

FIG. 5 is a block diagram of a method for defining multiple resourceelement allocations for positioning reference symbols from a singleCostas array.

FIG. 6 is a block diagram of a method for pruning columns of a 12×12Costas array in order to define resource element allocations forpositioning reference symbols on a resource block having fewer than 12non-control symbols.

FIG. 7 is a block diagram of a method for allocating resource elementlocations for positioning reference symbols using a pseudo-randomlyselected permutation matrix.

FIG. 8 is a block diagram of a method for allocating resource elementlocations for positioning reference symbols using matrices which arecyclic shifts of diagonal or anti-diagonal matrices.

FIG. 9 a block diagram of a method for allocating resource elementlocations for positioning reference symbols in resource blocks havingfewer than 12 non-control symbols by pruning the last columns ofmatrices which are cyclic shifts of diagonal or anti-diagonal matrices.

FIG. 10 is a block diagram of a method for allocating resource elementlocations for position reference symbols by randomly selecting a columnfor each row of matrix.

FIG. 11 is a block diagram of a method for using a fast fouriertransform and an inverse fast fourier transform to generate a timingreference signal from a time-domain single carrier direct-sequencespread spectrum signal.

FIG. 12 is a block diagram of a method for mapping positioning referencesymbols onto a unicast subframe containing common reference symbols.

FIG. 13 is a block diagram of a method for combining unicast ormulti-cast data in a positioning reference symbols in the same subframein which the resource blocks furthest from the carrier frequency areused to transmit data and the remaining resource blocks are used totransmit positioning reference symbols.

FIG. 14 is a logic flow diagram of steps executed by a wirelesscommunication device to process a downlink subframe containing apositioning reference signal, in accordance with an exemplary embodimentof the present invention.

Skilled artisans will appreciate that elements in the figures areillustrated for simplicity and clarity and have not necessarily beendrawn to scale or to include every component of an element. For example,the dimensions of some of the elements in the figures may be exaggeratedalone or relative to other elements, or some and possibly manycomponents of an element may be excluded from the element, to helpimprove the understanding of the various embodiments of the presentinvention.

DETAILED DESCRIPTION

Generally, the present invention encompasses an apparatus and method forcommunicating positioning reference signals based on an identifierassociated with a base station. In accordance with one embodiment, theapparatus is a wireless communication device that includes, inter alia,a receiver and a processor. The receiver is operable to receive at leasta section of one or more subframes, which may or may not be timecontemporaneous, from one or more base stations (e.g., providingwireless communication service to service coverage areas (e.g., cells)adjacent to a service coverage area in which the wireless communicationdevice is located). Each subframe includes transmission resources (e.g.,E-UTRA resource elements) that are divided in time over a symbol acrossa plurality of subcarriers to form a plurality of orthogonal frequencydivision multiplexed (OFDM) symbols. Each transmission resource istransmitted for a predetermined amount of time on a respective one ofthe subcarriers within an OFDM symbol. The OFDM symbols are arrangedinto at least a first set of OFDM symbols that includes a positioningreference signal (e.g., an observed time difference of arrival (OTDOA)waveform) and a second set of OFDM symbols that does not include apositioning reference signal, but which may optionally include acell-specific reference signal, and control information (e.g., aPhysical Downlink Control Channel or PDCCH).

In one embodiment, the processor is operable to determine a time ofarrival (TOA) of the positioning reference signal based on referencetiming information (e.g., produced from the wireless device's localoscillator) corresponding to a transmission from a particular basestation. Further, the processor may be operable to determine a time ofarrival of the positioning reference signal transmitted from a secondbase station based on reference timing information and to compute a timedifference of arrival (TDOA) of the positioning reference signal fromthe second base station relative to the first base station. In such anembodiment, the wireless communication device may further include atransmitter that is operable to communicate at least one of the time ofarrival and the time difference of arrival to a location server via abase station that is providing wireless communication service to thewireless communication device.

In an alternative embodiment, the apparatus may be a base stationoperable to encode, multiplex, and transmit a downlink subframecontaining a positioning reference signal, a cell-specific referencesignal, and optionally other information, such as control information.In such an embodiment, the base station includes, inter alia, aprocessor and a transmitter. The base station processor is operable toencode a positioning reference signal into a first set of transmissionresources (e.g., E-UTRA resource elements), encode information otherthan the positioning reference signal into a second set of transmissionresources, and multiplex the first set of transmission resources and thesecond set of transmission resources into a subframe that includes aplurality of OFDM symbols. The base station transmitter is operable totransmit to the subframe to wireless communication devices within acoverage range of the base station.

According to one embodiment, the first set of transmission resources ismultiplexed into a portion (i.e., some, but not all, OFDM symbols) of afirst set of OFDM symbols of the subframe (e.g., OFDM symbols forming aportion of the subframe that is not used for transmitting controlinformation (e.g., not forming a PDCCH region)) based on an identifierassociated with the base station and the second set of transmissionresources is multiplexed into a second set of OFDM symbols of thesubframe (e.g., OFDM symbols used for transmitting control information(e.g., a PDCCH)). Further, the first set of transmission resources maybe multiplexed into the first set of OFDM symbols such that thetransmission resources are multiplexed onto a subset of the subcarriersforming one or more OFDM symbols of the first set of OFDM symbols. Forexample, the first set of transmission resources may be multiplexed ontoone-sixth of the subcarriers forming an OFDM symbol (e.g., every sixthsubcarrier may be used for carrying a transmission resourcecorresponding to the positioning reference signal).

Embodiments of the present invention can be more readily understood withreference to FIG. 25, in which like reference numerals designate likeitems. FIG. 2 is an electrical block diagram of a wireless communicationsystem 200 providing wireless communication service to one or morewireless communication devices 201 in accordance with an exemplaryembodiment of the present invention. The wireless system 200 includes,inter alia, a plurality of base stations 203-205 (three shown forillustrative purposes), one or more wireless communication devices 201(one shown for illustrative purposes), and an optional location server207. Typically, the wireless system would include many other basestations and wireless communication devices. However, for purposes ofsimplicity in connection with describing the various features of thepresent invention, FIG. 2 depicts only one three base stations 203-205and one wireless communication device 201. In one embodiment, thewireless communication system 200 is a system that implements the E-UTRAstandard. Alternatively, the wireless system 200 may be any system thatutilizes orthogonal frequency division multiplexing and enables wirelessdevices 201 to autonomously determine their location or position withinthe system 200 or absolutely, or assist with such location determinationby, for example, reporting timing information (e.g., time of arrival(TOA) or time difference of arrival (TDOA) information) to the locationserver 207.

The wireless communication device 201 may be implemented as a mobiletelephone, a smart phone, a text messaging device, a handheld computer,a wireless communication card, a personal digital assistant (PDA), anotebook or laptop computer, a consumer premises equipment (CPE), or anyother communication device that has been modified or fabricated toinclude the functionality of the present invention. A smart phone is amobile telephone that has additional application processingcapabilities. For example, in one embodiment, a smart phone is acombination of (i) a pocket personal computer (PC), handheld PC, palmtop PC, or PDA, and (ii) a mobile telephone. Exemplary smart phones arethe iPHONE™ available from Apple, Inc. of Cupertino, Calif. and theMOTOROLA Q™ available from Motorola, Inc. of Schaumburg, Ill. A wirelesscommunication card, in one embodiment, resides or is insertable within aPC or a laptop computer. The term “wireless communication device,” asused herein and the appended claims, is intended to broadly cover manydifferent types of devices that can receive and/or transmit signals andthat can operate in a wireless communication system. For example, andnot by way of limitation, a wireless communication device can includeany one or a combination of the following: a cellular telephone, amobile phone, a smart phone, a two-way radio, a two-way pager, awireless messaging device, a laptop/computer, an automotive gateway, aresidential gateway, a personal computer, a server, a PDA, CPE, arouter, a cordless telephone, a wireless email device, a portable gamingdevice including a built-in wireless modem, and the like. An electricalblock diagram of an exemplary wireless communication device 201 isillustrated in FIG. 3.

The base stations 203-205 provide wireless communication service withinrespective geographic service coverage areas (e.g., cells). The basestations 203-205 may be co-located or diversely located. Whenco-located, the base stations 203-205 may provide wireless service torespective portions (e.g., sectors) of a single service coverage area(e.g., a cell). In one embodiment, the base stations are eNBs thatoperate in accordance with the E-UTRA standard.

The location server 207 is well known and is used to determine locationsof wireless communication devices 207 within the wireless communicationsystem 200. In one embodiment, the location server 207 usestriangulation or trilateration to locate a wireless communication device201 based on known locations of base stations 203-205 within the system200 together with time of arrival or time difference of arrivalmeasurements made and reported by the wireless communication device 201in response to receiving subframes carrying positioning referencesignals 209-211 from the base stations 203-205. Locations determined bythe location server 207 may be used for a variety of reasons, includingto locate a wireless device that has made an emergency call when suchdevice does not include GPS functionality or when GPS functionality isinoperable or impaired for any reason. While the location server 207 isshown a distinct entity from the base stations 203-205, it is notnecessary as certain base stations can also provide the logicalfunctionality of a location server 207.

FIG. 3 illustrates electrical block diagrams of the wirelesscommunication device 201 and an exemplary base station 301 usable in thewireless communication system 200 of FIG. 2. The base station 301 may beused to implement any of the base stations 203-205 of the wirelesscommunication system 200 of FIG. 2. Each base station 301 includes,inter alia, one or more transmit antennas 304-307 (four shown forillustrative purposes), one or more receive antennas 309, 310 (two shownfor illustrative purposes), one or more transmitters 312 (one shown forillustrative purposes), one or more receivers 314 (one shown forillustrative purposes), one or more processors 316 (one shown forillustrative purposes), and memory 318. Although illustrated separately,the transmitter 312 and the receiver 314 may be integrated into one ormore transceivers as is well understood in the art. By includingmultiple transmit antennas 304-307 and other appropriate hardware andsoftware as would be understood by those of ordinary skill in the art,the base station 301 may support use of a multiple input and multipleoutput (MIMO) antenna system for downlink (base station-to-wirelesscommunication device) communications. The MIMO system facilitatessimultaneous transmission of downlink data streams from multipletransmit antennas 304-307 depending upon a channel rank, for example asindicated by the wireless communication device 201 or as preferred bythe base station 301. A rank supplied by the wireless communicationdevice 201 assists or enables the base station 301 to determine anappropriate multiple antenna configuration (e.g., transmit diversity,open loop spatial multiplexing, closed loop spatial multiplexing, etc.)for a downlink transmission in view of the current downlink channelconditions.

The processor 316, which is operably coupled to the transmitter 312, thereceiver 314, and the memory 318, can be one or more of amicroprocessor, a microcontroller, a digital signal processor (DSP), astate machine, logic circuitry, any combination thereof, or any otherdevice or combination of devices that processes information based onoperational or programming instructions stored in the memory 318. One ofordinary skill in the art will appreciate that the processor 316 can beimplemented using multiple processing devices as may be required tohandle the processing requirements of the present invention and thevarious other functions of the base station 301. One of ordinary skillin the art will further recognize that when the processor 316 has one ormore of its functions performed by a state machine or logic circuitry,the memory containing the corresponding operational instructions can beembedded within the state machine or logic circuitry as opposed to beingexternal to the processor 316.

The memory 318, which may be a separate element as depicted in FIG. 3 ormay be integrated into the processor 316, can include random accessmemory (RAM), read-only memory (ROM), FLASH memory, electricallyerasable programmable read-only memory (EEPROM), removable memory, ahard disk, and/or various other forms of memory as are well known in theart. The memory 318 can include various components, such as, forexample, one or more program memory components for storing programminginstructions executable by the processor 316, one or more address memorycomponents for storing an identifier associated with the base station301 as well as for storing addresses for wireless communication devicescurrently in communication with the base station 301, and various datastorage components. The identifier may be derived from at least one ofan offset identifier specific to the base station, a base stationidentifier, a cell site identifier, a physical cell identifier, a globalcell identifier, a slot index, a subframe index, a system frame number,and/or a radio network transaction identifier. The program memorycomponent of the memory 318 may include a protocol stack for controllingthe transfer of information generated by the processor 316 over the dataand/or control channels of the system 200. It will be appreciated by oneof ordinary skill in the art that the various memory components can eachbe a group of separately located memory areas in the overall oraggregate memory 318 and that the memory 318 may include one or moreindividual memory elements.

In one embodiment, the base station transmitter 312, receiver 314, andprocessor 316 are designed to implement and support a wideband wirelessprotocol, such as the Universal Mobile Telecommunications System (UMTS)protocol, the E-UTRA protocol, the 3GPP Long Term Evolution (LTE)protocol, or a proprietary protocol, operating to communicate digitalinformation, such as user data (which may include voice, text, video,and/or graphical data) and/or control information, between the basestation 301 and the wireless communication device 201 over various typesof channels. In an E-UTRA system, an uplink data channel may be a PUSCH,an uplink control channel may be a physical uplink control channel(PUCCH), a downlink control channel may be a physical downlink controlchannel (PDCCH), and downlink data channel may be a physical downlinkshared channel (PDSCH). Uplink control information may be communicatedover the PUCCH and/or the PUSCH and downlink control information iscommunicated typically over the PDCCH.

When the base station 301 implements the E-UTRA standard, the basestation processor 316, in one embodiment, includes a logical channelcoding and multiplexing section for implementing channel coding andmultiplexing of control information and positioning reference signalsdestined for transmission over a downlink subframe 340. The channelcoding and multiplexing section is a logical section of the base stationprocessor 316, which performs the coding and multiplexing responsive toprogramming instructions stored in memory 318. The channel coding andmultiplexing section may include one channel coding block for encodingcontrol channel information (e.g., channel quality indicators,cell-specific reference symbols (CRS), rank indicators, and hybridautomatic repeat request acknowledgments (HARQ-ACK/NACK) into associatedtransmission resources (e.g., time-frequency resource elements) andanother block for encoding positioning reference signals and otherinformation typically communicated over the primary/secondarysynchronization channel (e.g., P/S-SCH) into associated transmissionresources. The channel coding and multiplexing section of the processor316 may include additional coding blocks for encoding various othertypes of information and/or reference symbols used by the wirelesscommunication device 201 for demodulation and downlink channel qualitydetermination. The channel coding and multiplexing section of theprocessor 316 also includes a channel multiplexing block thatmultiplexes the encoded information generated by the various channelcoding blocks into a subframe, which is supplied to the transmitter 312for downlink transmission.

Each wireless communication device 201 includes, inter alia, one or moretransmit antennas 320 (one shown for illustrative purposes), one or morereceive antennas 322, 323 (two shown for illustrative purposes), one ormore transmitters 325 (one shown for illustrative purposes), one or morereceivers 327 (one shown for illustrative purposes), a processor 329,memory 331, a local oscillator 332, an optional display 333, an optionaluser interface 335, and an optional alerting mechanism 337. Althoughillustrated separately, the transmitter 325 and the receiver 327 may beintegrated into one or more transceivers as is well understood in theart. By including multiple receive antennas 322, 323 and otherappropriate hardware and software as would be understood by those ofordinary skill in the art, the wireless communication device 201 mayfacilitate use of a MIMO antenna system for downlink communications.

The wireless communication device transmitter 325, receiver 327, andprocessor 329 are designed to implement and support a wideband wirelessprotocol, such as the UMTS protocol, the E-UTRA protocol, the 3GPP LTEprotocol or a proprietary protocol, operating to communicate digitalinformation, such as user data (which may include voice, text, video,and/or graphical data) and/or control information, between the wirelesscommunication device 201 and a serving base station 301 over control anddata channels. In an E-UTRA system, an uplink data channel may be aPUSCH and an uplink control channel may be a PUCCH. Control informationmay be communicated over the PUSCH and/or the PUCCH. Data is generallycommunicated over the PUSCH.

The processor 329 is operably coupled to the transmitter 325, thereceiver 327, the memory 331, the local oscillator 332, the optionaldisplay 333, the optional user interface 335, and the optional alertingmechanism 337. The processor 329 utilizes conventional signal-processingtechniques for processing communication signals received by the receiver327 and for processing data and control information for transmission viathe transmitter 325. The processor 329 receives its local timing andclock from the local oscillator 332, which may be a phase locked looposcillator, frequency synthesizer, a delay locked loop, or other highprecision oscillator. The processor 329 can be one or more of amicroprocessor, a microcontroller, a DSP, a state machine, logiccircuitry, or any other device or combination of devices that processesinformation based on operational or programming instructions stored inthe memory 331. One of ordinary skill in the art will appreciate thatthe processor 329 can be implemented using multiple processors as may berequired to handle the processing requirements of the present inventionand the various other included functions of the wireless communicationdevice 201. One of ordinary skill in the art will further recognize thatwhen the processor 329 has one or more of its functions performed by astate machine or logic circuitry, the memory containing thecorresponding operational instructions can be embedded within the statemachine or logic circuitry as opposed to being external to the processor329.

The memory 331, which may be a separate element as depicted in FIG. 3 ormay be integrated into the processor 329, can include RAM, ROM, FLASHmemory, EEPROM, removable memory (e.g., a subscriber identity module(SIM) card or any other form of removable memory), and/or various otherforms of memory as are well known in the art. The memory 331 can includevarious components, such as, for example, one or more program memorycomponents for storing programming instructions executable by theprocessor 329 and one or more address memory components for storingaddresses and/or other identifiers associated with the wirelesscommunication device 201 and/or the base stations 203-205. The programmemory component of the memory 331 may include a protocol stack forcontrolling the transfer of information generated by the processor 329over the data and/or control channels of the system 200, as well as forcontrolling the receipt of data, control, and other informationtransmitted by the base stations 203-205. It will be appreciated by oneof ordinary skill in the art that the various memory components can eachbe a group of separately located memory areas in the overall oraggregate memory 331 and that the memory 331 may include one or moreindividual memory elements.

The display 333, the user interface 335, and the alerting mechanism 337are all well-known elements of wireless communication devices. Forexample, the display 333 may be a liquid crystal display (LCD) or alight emitting diode (LED) display and associated driver circuitry, orutilize any other known or future-developed display technology. The userinterface 335 may be a key pad, a keyboard, a touch pad, a touch screen,or any combination thereof, or may be voice-activated or utilize anyother known or future-developed user interface technology. The alertingmechanism 337 may include an audio speaker or transducer, a tactilealert, and/or one or more LEDs or other visual alerting components, andassociated driver circuitry, to alert a user of the wirelesscommunication device 302. The display 333, the user interface 335, andthe alerting mechanism 337 operate under the control of the processor329.

Referring now to FIGS. 2-13, operation of a base station 301 (which maybe any of the base stations 203-205 in the exemplary wireless system200) occurs substantially as follows in accordance with the presentinvention. At a predetermined time (e.g., periodically oraperiodically), the base station processor 316 optionally encodes (401)control information into a first set of transmission resources of areference block of transmission resources allocated for transmission.Where the base station 301 implements the E-UTRA or LTE standard, theallocated block of transmission resources include time-frequencyresource elements to be multiplexed into a subframe of OFDM symbolsforming one or more transmission channels. For each transmit antenna,the set of transmission resources form a two-dimensional resourceelement grid in time and frequency. In frequency, the transmissionresources are typically mapped into different subcarriers within eachOFDM symbol across the transmission bandwidth. Multiple such OFDMsymbols comprise a subframe. In the E-UTRA standard, at least twosubframe structures—one with 14 OFDM symbols referred to as a “normal CPsubframe” and one with 12 OFDM symbols referred to an “extended CPsubframe”—are defined. The subframe may be further divided into twohalves or slots with an equal number of OFDM symbols. A subframe maycarry one or more transmission channels such as control channel (e.g.,PDCCH, PCFICH, PHICH), data channel (e.g., PDCCH), broadcast channel(e.g., PBCH), synchronization channel (e.g., P/S-SCH), or any otherchannel. In addition to these channels, the subframe may include acell-specific reference signal, a dedicated or UE-specific referencesignal, a positioning reference signal, or any other reference signal.

In E-UTRA, there are two types of subframes and one of these is theunicast subframe where the Cell-specific Reference symbols are sent inboth the slots of the subframe. Some other subframes may be occasionallycharacterized as special sub-frames or non-unicast subframes. An exampleof such subframes are Multimedia Broadcast Multicast Service over aSingle Frequency Network (MBSFN) subframe, wherein the subframestructure is different from a unicast subframes. In the specialsubframes or non-unicast subframes, the first one or two (or possiblyzero) OFDM symbols may contain the PDCCH and reference symbols, whereasthe rest of the subframe including the RS structure may be differentthan a unicast subframe. For instance, the multimedia multicastbroadcast over single frequency network (MBSFN) subframe is a type ofnon-unicast subframe wherein the rest of the subframe may be blanked orempty and these empty resources can be used to transmit positioningreference symbols. The non-unicast (or special subframe) signalingpattern may be part of system configuration or System InformationBroadcast (SIB) message and may be defined on a Radio-frame level (10subframes) or for a group of Radio Frame level. In one embodiment, thebase station processor 316 encodes control information into resourceelements to be multiplexed into a portion of the first two OFDM symbolsof the subframe.

The coded control information may include downlink assignments or uplinkgrants, control channel duration, and hybrid automatic repeat requestacknowledgments (HARQ-ACK/NACK). In addition to the control information,a set of symbols corresponding to a cell-specific reference signal maybe included in the subframe. The cell-specific reference signal may beused for channel estimation, demodulation, delay tracking,mobility-related measurements, and other purposes by the wireless device201. When included, the sequence of symbols corresponding to the cellspecific reference signal and the time-frequency locations occupied bythe symbols may be derived from an identifier associated with the basestation 301. Such identifier may include a physical cell identifier(PCID), a slot index and/or a symbol index, all of which are well knownin the art particularly in connection with the E-UTRA standard. Inaddition, the subcarrier offset used for mapping the symbols of thecell-specific reference signal into an OFDM symbol may be derived fromthe physical cell identifier.

In addition to optionally encoding control information and thecell-specific reference signal into transmission resources, the basestation processor 316 encodes (403) a positioning reference signal intoa second set of transmission resources. The base station processor 316encodes the positioning reference signal into a portion of a pluralityof resource blocks where each resource block comprises a two-dimensionalgrid of approximately 12 contiguous subcarriers in frequency and all theOFDM symbols of the subframe in time where each OFDM symbol isassociated with a normal or an extended cyclic prefix as described inthe E-UTRA standard. For illustration purposes, a typical resource blockis defined as the resources available in 12 subcarriers and all OFDMsymbols of the subframe. It is noted that the resource block dimensionsmay be varying as some of the subcarriers of OFDM symbols may be usedfor other purposes such as transmission of pre-determined controlprimary broadcast channel, or synchronization channels, etc. The numberof resource blocks available for transmission on the downlink (i.e., thelink between the base station 301 and wireless device 201) may bedependent on the transmission bandwidth. The base station processor 316may be programmed to encode the positioning reference signal into asubset of the available OFDM symbols in the subframe. In one exemplaryembodiment, the base station processor 316 encodes the positioningreference signal into a portion of 600 resource elements of an OFDMsymbol of the subframe when the downlink transmission bandwidth is 10MHz. Further, not all of the subcarriers on these OFDM symbols may beused for carrying the transmission resources corresponding to thepositioning reference signal. In one example, every sixth subcarrier isused for transmitting the symbols of the positioning reference signal.After the entire block of transmission resources have been multiplexedinto the subframe, the base station transmitter transmits (415) thesubframe via one or more of the antennas 304-307.

Referring first to FIG. 5, such figure depicts subframes 501, 502generated and transmitted by base stations providing communicationservice to service coverage areas (e.g., cells or cell sectors) adjacentto or neighboring the service coverage area in which the wirelesscommunication device 201 receiving the subframes is located. Forexample, in the wireless system 200 illustrated in FIG. 2, if basestation 204 is supplying communication service to the wireless device201 (i.e., the wireless device 201 is located in the service coveragearea of base station 204 and, therefore, base station 204 is the servingstation for the wireless device 201), then the service coverage areasserviced by base stations 203 and 205 may be considered neighboringservice coverage areas and base stations 203 and 205 may be consideredneighboring base stations. One of ordinary skill in the art will readilyappreciate and recognize that the quantity of neighboring servicecoverage areas and base stations may exceed to the two illustrated inFIG. 2. Accordingly, the approach disclosed herein for subframe creationmay be used by every base station in the applicable wireless systembecause, at some point in time, each base station serves a servicecoverage area neighboring a service coverage area in which at least onewireless communication device is located.

When a positioning reference signal is to be included, the resourceelements for carrying the positioning reference signal may be allocatedin either a pre-determined fashion (e.g., as defined in the E-UTRA orLTE standards), semi-statically through broadcast (e.g. via signaling ina master information block (MIB) or system information block (SIB)) orin a user-specific message (e.g., radio resource control measurementconfiguration message), dynamically (e.g., via control channel signalingin PDCCH), or by higher layer signaling (e.g., location server protocoldata units. In one embodiment, the mapping of which OFDM symbol of thesubframe 501, 502 contains the positioning reference signal is based onan identifier associated with the base station 203, 205, which may takeinto account the base station's location in the system 200 and the reusepattern of the various subcarriers used to generate OFDM symbols of thesubframe. The identifier may be one or more of an offset identifier, abase station identifier, a cell site identifier, a physical cellidentifier (PCID), a global cell identifier (GCID), a symbol index, aslot index, a subframe index, a system frame number (SFN), and/or aradio network transaction identifier (RNTI).

In a planned deployment, it would be desirable to allocate eNBs in thesame vicinity sets of resource elements for positioning referencesymbols which are disjoint in the sense that no resource element of theset allocated to a first eNB for transmission of positioning referencesymbols belongs to any of the sets of resource elements allocated to itsneighboring eNBs. Two sets of resource elements which are disjoint canalso be referred to as orthogonal. In some instances, it is not possibleto define a number of disjoints sets of resource elements that equals orexceeds the number of eNBs in a particular region. In some instances, aregion can be defined as the set of eNBs “hearable” by a UE. In theseinstances, it is then desirable to define sets of resource elements forpositioning reference symbols which have minimum overlap and which aresufficient in number to equal or exceed the number of eNBs in aparticular region. It should be noted that in this context, the degreeof overlap between two sets of resource elements is equal to the numberof resource elements common to both sets.

In an unplanned deployment, there is in general no way to ensure thatthe set of resource elements allocated for positioning reference symbolsto one eNB will be orthogonal or nearly orthogonal to the set ofresource elements allocated to one of its neighbors. In order to protectagainst the permanent assignment of two different sets of resourceelements with large overlap to two adjacent eNBs, it may be desirablefor each eNB to randomly or pseudo-randomly re-select the set ofresource elements to be used to transmit positioning reference symbolsprior to each positioning subframe transmission. If the number of setsof allowed resource allocations is small, then there is a significantlikelihood that two adjacent eNBs will select the same resourceallocation for the transmission of positioning reference symbols, and insuch an instance, it will be difficult for the UE to extract timinginformation due to the resulting interference. In order to minimize thelikelihood that any two eNB's will select the same set of resourceelements for the transmission of positioning reference symbols, thenumber of allowed sets of resource elements should be large, and to thegreatest extent possible, these sets should be orthogonal (no overlap)or nearly orthogonal (small overlap).

There are many parameters and issues to consider when defining sets ofresource elements for the purpose of transmitting positioning referencesymbols, and these include (but are not limited to) the following, allof which are discussed below: (i) the number of OFDM symbols within thepositioning subframe containing positioning reference symbols; (ii) thenumber of subcarriers within a resource block containing positioningreference symbols; (iii) the total number of resource elements allocatedfor positioning reference symbols within the subframe; and (iv) thecomplexity of signal generation and detection for the positioningsubframes.

A significant problem for TDOA-based location is that it requires the UEbe able to “hear” the transmissions of at least 3 eNB's which are notco-sited, and most studies indicate that is the “hearability” problemwhich limits the performance of TDOA-based location, and this is closelytied to the number of reference symbols containing positioning referencesymbols (i). In general, the amount of energy associated with thetransmission of the positioning reference symbols within the positioningsubframe is proportional to the number of OFDM symbols within thepositioning subframe which contain positioning reference symbols. Thus,when defining sets of resource elements for the purpose of transmittingpositioning reference symbols, it seems to be advantageous to ensurethat each set includes resource elements from each of the symbols.

Another issue to consider when defining sets of resource elements to beallocated for positioning resource elements is the resolution of theresulting time estimate and this is related to the number of subcarrierscontaining positioning reference symbols (ii) and their distributionthroughput the subframe. Several factors contribute to the resolutionincluding the both the width of the autocorrelation peak and the ratioof the autocorrelation peak to the strongest sidelobes. In general, itcan be found that in order to minimize the width of the autocorrelationpeak, it is sufficient to allocate reference elements for positioningreference symbols in the outermost resource blocks (highest and lowestfrequency RBs). However, in order to maximize the ratio of the magnitudeautocorrelation peak to that of the sidelobes, it is desirable toallocate resource elements for positioning reference symbol throughoutthe entire bandwidth. More specifically, it is desirable to select setsof resource elements for positioning reference symbols such that thenumber of subcarriers within each resource block containing at least oneof these resource elements is maximized. In general, it is desirable tomaximize the ratio of the magnitude of the autocorrelation peak to thesidelobes as this will minimize the likelihood that a falseautocorrelation peak is selected (resulting in an incorrect timingestimate) in the presence of interference and noise.

The total number of resource elements within a set of resource elementsallocated for positioning reference symbols (iii) determines thespreading or processing gain achievable against another eNB that isassigned either this same set of resource elements or another set ofresource elements which overlaps with this first set. In general, randomor pseudo-random spreading or scrambling will be applied to thepositioning reference symbols, such that a UE with knowledge of thisspreading or scrambling sequence can still extract the time of arrivalof the signal from each eNB with some degree of accuracy. As the totalnumber of resource elements allocated for positioning reference symbolsis increased, so does the achievable processing gain against other eNB'swith either the same or overlapping resource allocations for positioningreference symbols. However, it must be noted that as the number resourceelements allocated for positioning reference symbols is increased, thenumber of orthogonal allocations of resource elements which can bedefined is decreased, and the amount of overlap between non-orthogonalallocations is increased. Thus, as the number of resource elementsallocated for positioning reference symbols is increased, there is aclear tradeoff between the achievable processing gain and the number ofsets of orthogonal or nearly orthogonal resource elements. In anunplanned system, it is the number of such sets of resource elementsthat will determine the likelihood that two neighboring eNB's select thesame set of resource elements for the transmission of positioningreference symbols.

A last issue to consider in the definition of sets of resource elementsto be used for the transmission of positioning reference symbols is thecomplexity of signal generation and detection. In general, there is nosimple measure of complexity as it is architecture dependent. Tradeoffsof complexity can be defined separately for the transmitter and thereceiver, and may include memory requirements. A further issue toconsider is whether signaling support is required to make implementationpractical, or if not, the difference in complexity with and withoutsignaling support.

In FIGS. 5-12, various methods are given for defining sets of resourceelements to be used for the transmission of positioning referencesymbols in positioning subframes. The methods indicated in FIGS. 5-12and described below take into consideration the design and performancetradeoffs identified in (i-iv) as described above.

In order to simplify the description of the sets of resource elements tobe used to transmit positioning reference symbols within a positioningsubframe, we define a template matrix having 0-1 entries such thatnumber of rows of the template matrix is equal to the number ofsubcarriers in a resource element block and the number of columns isequal to the number of OFDM symbols in the subframe. The set of resourceelements within a resource block that will be allocated for thetransmission of positioning reference symbols are indicated by thelocations of the non-zero entries within the template matrix, where therow of a particular non-zero entry denotes the subcarrier and the columnof the entry denotes the symbol within the subframe.

FIG. 5 is a block diagram of a method for defining multiple resourceelement allocations for positioning reference symbols from a base Costasarray. A first 0-1 valued intermediate matrix is obtained by cyclicallyshifting the base Costas array of dimension N×N horizontally andvertically. This first intermediate matrix is then modified to produce asecond intermediate matrix by inserting K rows of zeros in between eachgroup of K consecutive rows and by appending K rows of zeros to the topor the bottom of the matrix, where K>1 and K is an integer divisor of N.The template matrix used to define the set of resource elements to beused for the transmission of positioning reference symbols is then setequal to a circular shift of the second intermediate matrix, where thenumber of cyclic shifts in each dimension of the base Costas array toproduce the first intermediate matrix and the vertical shift of thesecond intermediate matrix are determined from any one of the following:the site identifier of the base station; the physical cell identity ofthe base station; the global cell identity of the base station; thesystem frame number; the slot number; the subframe number; the symbolindex; the resource element block index; the radio network transactionidentity; or information signaled by the serving base station.

FIG. 6 is a block diagram of a method for pruning columns of a 12×12Costas array in order to define resource element allocations forpositioning reference symbols on a resource block having fewer than 12non-control symbols. With this method, we define 12 mutually orthogonalsets of resource elements by cyclically shifting the Costas array eitherhorizontally or vertically. The corresponding template matrices are thengenerated by pruning the last two columns of the cyclically shifted12×12 Costas matrices. The advantage of this method is that the singlebase 12×12 Costas array can be used to generate 12 orthogonal sets ofresource elements by cyclically shifting the Costas array eitherhorizontally or vertically. If alternatively, a N×N Costas array were tobe used, where N<12 is equal to the number of non-control symbols in thesubframe, it would only be possible to define K mutually orthogonal setsof resource elements to be used for the transmission of positioningreference symbols. More generally, the 12×12 Costas array can becyclically shifted horizontally and vertically to define 144 distinctmatrices, each of which, after pruning of the last two columns, can beused to define a set of resource elements for the transmission ofpositioning reference symbols. Conversely, for N<12, a base N×N Costasarray can be used to generate at most 121 distinct matrices that can beused to define sets of resource elements for the transmission ofreference symbols.

FIG. 7 is a block diagram of a method for allocating resource elementlocations for positioning reference symbols using a pseudo-randomlyselected permutation matrix. In this embodiment, the 0-1 template matrixis a pseudo-random permutation matrix (a square matrix with preciselyone non-zero element in each row and column, where the non-zero elementis equal to 1). The particular permutation matrix (there are N!permutation matrices for an N×N matrix) is determined from a mappingfunction of a pseudo-random number generator and any one of thefollowing: the site identifier of the base station; the physical cellidentity of the base station; the global cell identity of the basestation; system frame number; the slot number; the subframe number; thesymbol index; the resource element block index; the radio networktransaction identity; or information signaled by the serving basestation.

FIG. 8 is a block diagram of a method for allocating resource elementlocations for positioning reference symbols using matrices which arehorizontal or vertical cyclic shifts of diagonal matrices. In thisembodiment, the 0-1 template matrix is either a cyclically shifteddiagonal matrix or a cyclically shifted anti-diagonal matrix, where theamount of cyclic shift is determined from any one of: a site identifierof the base station; a physical cell identity of the base station; aglobal cell identity of the base station; a system frame number; asubframe number; resource element block index; a radio networktransaction identity; or information signaled by the serving basestation. Note that the number of orthogonal matrices generated with thismethod is equal to the dimension of the diagonal matrix.

FIG. 9 a block diagram of a method for allocating resource elementlocations for positioning reference symbols in resource blocks havingfewer than 12 non-control symbols by pruning the last columns ofmatrices which are cyclic shifts of diagonal or anti-diagonal matrices.In this embodiment, the 0-1 template matrix is either a cyclicallyshifted diagonal matrix or a cyclically shifted diagonal matrix fromwhich the last columns have been pruned. Alternatively, the templatematrices can be generated by appending two rows of zeros to the bottomof a diagonal or anti-diagonal matrix and generating all possiblevertical circular shifts. In this example, the number of orthogonalmatrices generated is 12, while the dimension of the diagonal matrixthat is shifted is 10.

FIG. 10 is a block diagram of a method for allocating resource elementlocations for position reference symbols by pseudo-randomly selectingone column for each row of the matrix and placing a 1 in this location.All other locations in the matrix are zero-valued. In this embodiment,the 0-1 template matrix is determined using a pseudo-random numbergenerator in the manner indicated, where further the pseudo-randomnumber generator uses as its input any one of: the site identifier ofthe base station; the physical cell identity of the base station; theglobal cell identity of the base station; the system frame number; thesubframe number; the resource element block index; the radio networktransaction identity; or information signaled by the serving basestation.

FIG. 11 is a block diagram of a method for using a Fast-Fouriertransform and an inverse Fast-Fourier transform to generate a timingreference signal from a time-domain single carrier direct-sequencespread spectrum signal. In this embodiment, the reference signal on afirst set of OFDM symbols is obtained by taking Fast-Fourier Transformof a time-domain sequence obtained from a pseudo-random sequencegenerator, where the initialization of the pseudo-random numbergenerator is determined from any one of: a site identifier of the basestation; a physical cell identity of the base station; a global cellidentity of the base station; a system frame number; a subframe number;a resource element block index; a radio network transaction identity; orinformation signaled by the serving base station.

FIG. 12 is a block diagram of a method for mapping positioning referencesymbols onto a unicast subframe containing common reference symbols. Inthis particular embodiment, resource elements in OFDM symbols containingCRS are not allocated for the transmission of positioning referencesymbols. In general, resource elements in OFDM symbols containing CRScan be allocated for positioning reference symbols, but resourceelements used to transmit CRS cannot be used. In an alternateembodiment, the resource elements not used for transmission of eitherpositioning reference signal or the CRS may be used for transmission ofdata resource elements. The data resource elements may correspond to asequence of symbols of a PDSCH transmission.

FIG. 13 is a block diagram of a method for combining unicast ormulti-cast data and positioning reference symbols in the same subframein which the resource blocks furthest from the carrier frequency areused to transmit data and the remaining resource blocks are used totransmit positioning reference symbols. In this particular example, the600 center resource elements (center 50 resource blocks) of positioningcan only be allocated for positioning reference symbols, while theresource elements in resource blocks outside of this region can be usedfor PDSCH transmissions.

The embodiments in FIG. 7, FIG. 8 and FIG. 10 can be extended to thecase of a non-MBSFN subframe (or normal subframe) with either normal CPor with extended CP. PRS cannot be transmitted at maximum power if istransmitted on the same symbol as cell-specific reference signal (CRS)is transmitted. In addition, PRS might have to be transmitted atdifferent powers on different symbols within the same subframe whichmight be undesirable from an implementation point of view. Therefore,one option is to not transmit PRS on a CRS-bearing OFDM symbol. Assumingthat the number of control symbols is two, there are 9 symbols and 7symbols in a normal CP subframe and in an extended CP subframe,respectively, that do not carry CRS. For these cases, pseudo-randomlygenerated permutation matrices of order N×N can be used for populatingPRS, where N is equal to the number of available OFDM symbols (i.e.,without CRS) in each case. N=9 for normal CP and N=7 for extended CP.Once a matrix is chosen for a particular PCID corresponding to a timeinstant, the PRS pattern is repeated in the frequency domain once everyN subcarriers. The number of OFDM symbols available depends both on thenumber of control symbols in the subframe and on the number of transmitantennas used by the eNB. Table 1 summarizes the number of OFDM symbolsavailable for PRS transmission for the different cases where NCtrl isequal to the number of control symbols in the subframe.

TABLE 1 Number of symbols N available for PRS transmission 1 Tx or 2 Tx4 Tx Subframe Type/CP Type NCtrl = 1 NCtrl = 2 NCtrl = 1 or 2 Normalsubframe/Normal CP 10 9 8 Normal subframe/Extended CP 8 7 6 MBSFNsubframe/Extended CP 11 10 10

For embodiment of FIG. 7, the pseudo-random number generator chooses anelement from the set of all possible N! permutation matrices. For theembodiment of FIG. 8, the pseudo-random number generator chooses anelement from the set of 2N distinct matrices formed by different cyclicshifts of the diagonal matrix and the anti-diagonal matrix. For theembodiment of FIG. 10, the pseudo-random number generator chooses anelement from the set of all possible N^(N) 0-1 matrices. For theembodiments in FIG. 7, FIG. 8 and FIG. 10, the dimension of the pattern(i.e., N) may be fixed in the specification for a given configuration(e.g., non-MBSFN subframe, extended CP, 2 Tx antenna) as indicated inTable 1 corresponding a fixed number of control symbols (e.g., NCtrl=1or NCtrl=2).

For transmission of the positioning reference signal, a certain subsetof all possible subframes designated as “positioning subframes” can bereserved. Of all the available positioning subframes, a base station maychoose to transmit PRS signals on a subset of these subframes to allowfor time reuse. A base station may determine whether or not to transmitPRS on a PRS subframe based on either (i) a pseudo-random numbergenerator that uses any one of: a site identifier of the base station; aphysical cell identity of the base station; a global cell identity ofthe base station; a system frame number; a subframe number; or a radionetwork transaction identity; or alternately based on (ii) a inter-basestation coordination message exchanged with another base station. Foroption (i), the pseudo-random number may, in addition to the listedparameters, be configured as a function of the number of OFDM symbolsavailable for PRS transmission in the PRS subframe. When the positioningreference signal is transmitted on fewer symbols (e.g., for 4 Tx caseextended CP non-MBSFN subframe has 6 symbols available compared to 1Tx/2 Tx MBSFN subframe which has 10), the number of orthogonal patternsis smaller. It might be useful to transmit PRS less often and therefore,the pseudo-random number generator may be configured to generate fewertransmissions of the PRS signals within the reserved subframes.

For the embodiments in FIG. 7, FIG. 8 and FIG. 10, an alternate approachof using the template matrix for transmission of the positioningreference signal resource elements may be used as outlined below.Suppose that there are N non-control OFDM symbols in a positioningsubframe. Also, suppose that there are no CRS-bearing OFDM symbols amongthe non-control OFDM symbols in the subframe. A N×N template matrix isgenerated as (i) a permutation matrix for the embodiment of FIG. 7, (ii)a shifted diagonal or a shifted anti-diagonal matrix for the embodimentof FIG. 8, or (iii) a 0-1 matrix with pseudo-random row/column selectionfor the embodiment of FIG. 10. A correspondence from the rows andcolumns of the template matrix respectively to the subcarriers andnon-control OFDM symbols of a resource element block in the positioningsubframe is established where a positioning reference signal resourceelement is transmitted on a subcarrier whose shift is equal to the rowindex of a non-zero element of the template matrix for each symbol.Next, suppose that there are CRS-bearing OFDM symbols in the non-controlregion of the subframe. The procedure described earlier can be re-usedexcept that, a subcarrier location determined for positioning referencesignal on a given symbol is not used for PRS transmission if it overlapswith a resource element allocated for CRS transmission on that symbol.In other words, PRS transmission is punctured on resource elementsdesignated for CRS. One issue with this approach is that, since somesymbols carry both CRS and PRS, the transmission power has to be sharedbetween resource elements corresponding to both CRS and PRS. It would bedesirable to transmit PRS at the maximum possible transmit power onsymbols not carrying CRS to achieve the best possible hearability.Therefore, the punctured mapping approach may result in the transmissionof a positioning subframe with (a) PRS transmission on OFDM symbols notcarrying CRS at a first power level, and (b) PRS transmission onCRS-bearing OFDM symbols at a second power level. In such a scenario, itmight be beneficial if the user equipment were to know the difference inthe two power levels. In one embodiment, the power delta (equal to thedifference between the first and the second power levels) can besignaled by the serving base station on a system information broadcastor on a dedicated control message (e.g., radio resource controlmessage). The user equipment may use this information to aid itsreceiver processing towards estimation of time-difference of arrival.

The positioning reference signals (e.g., observed time difference ofarrival (OTDOA) waveforms) from neighboring base stations 203, 205 canbe used jointly such that there is time-domain separation betweentransmissions of such signals from neighboring base stations 203, 205.Further, not all of the subcarriers or resource elements on the OFDMsymbols carrying the positioning reference signal may be used fortransmission. The set of resource elements carrying the positioningreference signal in an OFDM symbol may determined as a function of anidentifier associated with the transmitting base station which may bederived from at least one of a physical cell identifier (PCID), a basestation identifier, a cell site ID, a global cell identifier (GCID), asystem frame number (SFN), a symbol index, a slot index, a subframeindex, a radio network transaction identifier (RNTI) or any otherapplicable identifier. To enhance the timing extraction support from thepositioning reference signal, the sequence of symbols used for encodingthe transmission resources corresponding to the positioning referencesignal may be generated in a way to avoid secondary cross-correlationpeaks. Gold sequence generators may be used for generating an in-phase(I) stream and a quadrature (Q) stream of and a QPSK sequence may beconstructed from the I-Q streams. The initializers or the seeds for theregisters in the Gold sequence generator may be derived from anidentifier associated with the base station. The identifier may bederived from at least one of a physical cell identifier (PCID), a basestation identifier, a cell site ID, a global cell identifier (GCID), asystem frame number (SFN), a symbol index, a slot index, a subframeindex, a radio network transaction identifier (RNTI) or any otherapplicable identifier. Further, such an identifier may be used to derivean offset that is used as the starting point of extraction of asubsequence from the so-derived QPSK sequence. This QPSK sequence maythen be used for encoding the transmission resources used fortransmitting the positioning reference signal. In another example, anorthogonal set of time-frequency resources for transmission ofpositioning reference symbols (PRS) may be identified for use in a setof coordinating base stations. Thus, coordinating base stations canorthogonalize their PRS transmissions by selecting different indicesinto the orthogonal set of time-frequency resources and this index mayalso be considered as part of the identifier.

Those of ordinary skill in the art will readily appreciate and recognizethat various other time and frequency re-use approaches forcommunicating positioning reference signals in overlapping ornon-overlapping time resources can be envisioned taking into account theprinciples described herein and particularly above with respect to thesubframe structures illustrated in FIGS. 5-13. Accordingly, theexemplary subframe structures discussed above with respect to FIGS. 5-13are merely illustrative in nature and should not be construed or used tolimit the present invention as defined by the appended claims.

Referring now to FIGS. 2, 3 and 5-13, operation of an exemplary wirelesscommunication device 201 to process subframes (containing positioningreference signals in accordance with one embodiment of the presentinvention will be described. Prior to receipt of subframes containingpositioning reference signals, the wireless device receiver 327 receives(801), from a base station serving the service coverage area in whichthe wireless device 201 is located (serving base station), one or moreidentifiers associated with the base stations that will be transmittingthe subframes, particularly identifiers associated with base stationsserving service coverage areas (e.g., cells or sectors) neighboring theservice coverage area in which the wireless communication device 201 ispresently located. The identifiers may be, for example, beacon codes oridentifiers, offset identifiers, base station identifiers, cell siteidentifiers, PCIDs, GCIDs, subframe indexes, SFNs, and/or a RNTIs andmay have been received as part of a broadcast control message, such asan MIB or SIB, from the serving base station. For example, theidentifiers associated with the base stations 203, 205 servingneighboring service coverage areas may have been communicated as part ofa neighbor cell list transmitted from the wireless device's serving basestation 204 (assuming, for example, that the wireless device 201 isbeing serviced by base station 204 in FIG. 2). Alternatively, theidentifier may be encoded into a subframe containing the positioningreference signal (e.g., PDCCH or other control information contained inthe subframe).

In addition to receiving identifiers associated with base stationsserving neighboring service coverage areas (neighbor base stations), thewireless communication device receiver 327 receives (803) one or moresubframes containing positioning reference signals from one or more basestations (e.g., base stations 203 and 205). For example, the wirelessdevice 201 may receive a subframe as illustrated in FIGS. 5-7. Thereceiver 327 provides a baseband version of the received subframe to theprocessor 329 for processing in accordance with the present invention.The processor 329 first extracts a base station identifier or anotheridentifier associated with the base station before it can receive thesubframe bearing the positioning reference signal. The processor 329 mayreceive the identifier together with a neighbor cell list or other listof identifiers associated with neighbor base stations.

Upon receiving the subframe, the wireless device processor 329determines (805) whether the subframe originated from a base stationfrom which the wireless device processor 329 can process a positioningreference signal to estimate timing information (e.g., time of arrivalinformation) useful in determining a location of the wireless device 201and whether the subframe contains a positioning reference signal. Thepositioning reference signal may not be transmitted on all subframes,but rather may be transmitted in a certain subset of all subframes usedfor transmission by the base station. The base station may indicate tothe wireless device 201 which subframes bear the positioning referencesignal. The base station may indicate which subframes are used forpositioning reference signal transmission through a second identifierassociated with the base station. This second identifier may bepre-determined (e.g., specified in a 3GPP specification), or alternatelyincluded in a system broadcast message or a UE-specific control message(e.g., radio resource control measurement configuration message) by thebase station. Subsequently, the wireless device processor 329 candetermine whether a subframe contains a positioning reference signal ornot. Further, it can process a positioning reference signal on subframesthat carry such a signal to estimate timing information (e.g., time ofarrival of the first multipath component from the base station) usefulin determining a location of the wireless device 201. When eitheridentifier indicates that either the subframe does not contain aposition reference signal or that the information within the subframe(e.g., a positioning reference signal) cannot be used for determiningposition-related timing information (e.g., the identifier does notcorrespond to a desired base station), the processor 329 ignores (807)the received subframe. On the other hand, when the identifier indicatesthat information within the subframe (e.g., a positioning referencesignal) can be used for determining position-related timing information(e.g., the identifier is on a previously received neighbor cell list),the processor 329 processes the subframe and particular sets oftransmission resources therein to ultimately estimate timing information(e.g., time of arrival or observed time difference of arrivalinformation) that may be used in determining a location of the wirelessdevice 201.

In the event that the received subframe is from a base station fromwhich position-related timing information can be determined, thewireless device processor 329 determines (809) a set of transmissionresources in a non-control channel portion of the received subframe inwhich a positioning reference signal (e.g., an OTDOA waveform) wastransmitted based on an identifier associated with the base station. Forexample, the wireless device memory 331 may store a table that mapsidentifiers with OFDM symbol positions and characteristics (e.g., symboldurations and/or associated cyclic prefixes). The table may be updatedeach time the wireless device 201 receives a new neighbor cell list fromthe currently serving site or cell or when a new cell is detected andthe neighbor cell list is updated by the wireless device 201 in anautonomous fashion.

Based on the identifier (e.g., PCID) associated with the base stationfrom which the subframe was received, the wireless device processor 329demultiplexes the subframe to extract the set of transmission resources(e.g., time-frequency resource elements) carrying the positioningreference signal. In other words, based on the identifier associatedwith the base station that transmitted the subframe and the symbolmapping stored in the wireless device memory 331, the processor 329determines which OFDM symbol or symbols in the non-control channelportion of the frame contains the positioning reference signal.Additionally, the processor 329 determines, based on the stored mapping,whether the OFDM symbol or symbols containing the positioning referencesignal are of normal duration or normal or extended cyclic prefix underthe E-UTRA or LTE standard or have a special duration or associatedcyclic prefix (e.g., a multiple of a normal duration or a special,lengthier cyclic prefix). The processor 329 then processes (811) the setof transmission resources containing the positioning reference signal toestimate time of arrival information associated with the positioningreference signal based on reference timing information. For example, thewireless device processor 329 may determine a time of arrival of thepositioning reference signal based on a reference time or clock suppliedby the wireless device's local oscillator 332. Further, the wirelessdevice processor 329 may determine time of arrival from at least twobase stations from their respective positioning reference signaltransmissions based on a reference clock. In addition, the deviceprocessor 329 may compute the time difference of arrival correspondingto at least a subset of those base stations with the time of arrival ofone base station as the reference.

In one embodiment, after the transmission resources containing thepositioning reference signal have been processed and the timinginformation estimated, the wireless device processor 329 may determine(813) whether the wireless device 201 is in an autonomous locationdetermining mode in which the wireless device processor 329 determinesthe wireless device's location. If the wireless device 201 is in such anautonomous location mode, the wireless device processor 329 determines(815) the wireless device's location based on the timing informationcomputed for subframes received from multiple (two or more) basestations serving neighboring service coverage areas. In this case, thewireless device memory 331 stores the fixed locations of the system basestations and uses those fixed locations together with time of arrivalinformation to determine its location using known triangulation ortrilateralization methods. Alternatively, if the wireless device 201 isnot in an autonomous location determining mode and its location is to bedetermined by another device, such as the wireless system's locationserver 207, the wireless device communicates (817) the timinginformation (e.g., estimated times of arrival of positioning referencesignals received from two or more neighbor base stations) to thelocation-determining device via the wireless device's serving basestation. The wireless device in 201 may identify newly detectable cellson a certain carrier frequency autonomously and send a measurementreport to a base station to which it is connected. Alternatively, thebase station may send a neighbor cell list re-configuration message tothe UE. Either way, the wireless device 201 may update its neighbor celllist. A base station may send a UE-specific configuration message (e.g.,radio resource control measurement configuration message) requesting thewireless device 201 to determine the observed time difference of arrivalcorresponding to a subset of the neighboring base stations and reportthem. When the wireless device 201 may receive and decode such a messageand in response to it, determine the observed time difference of arrivalcorresponding to the subset of the configured neighboring base stations.The wireless device may then report these measurements to the basestation it is connected to.

To provide a further example of the operation of the wireless deviceprocessor 329 to assist in determining the wireless device's location,consider the system 200 of FIG. 2 under the circumstances in which basestation 204 is providing wireless service to the wireless device 201 andbase stations 203 and 205 are providing wireless service to servicecoverage areas (e.g., cells or sectors) neighboring the service coveragearea serviced by base station 204. In this case, the wireless device mayreceive subframes from both neighbor base stations 203, 205 In thisembodiment, each subframe includes a one millisecond (1 ms) block ofresource elements that are divided in time across a group of subcarriersto form OFDM symbols. Each resource element occupies a predeterminedamount of time (e.g., about 70 microseconds) on its respectivesubcarrier. The OFDM symbols of each subframe are arranged into a firstset of OFDM symbols into which control information has been encoded anda second set of OFDM symbols into which information other than controlinformation has been encoded. Such other information includes apositioning reference signal. In other words, each subframe may beconfigured to support a control channel (e.g., PDCCH) and asynchronization channel (e.g., a P/S-SCH).

After receiving the subframes, the wireless device processor 329determines, for each subframe, a set of resource elements (andanalogously a set of OFDM symbols) in which a positioning referencesignal was transmitted based on an identifier associated with the basestation 203, 205 from which the particular subframe was received. Theset of OFDM symbols carrying the positioning reference signal from basestation 203 is preferably orthogonal to the set of OFDM symbols carryingthe positioning reference signal from base station 205. The differencein positioning of the positioning reference signal resource elementsand/or OFDM symbols either in time or frequency is stored in thewireless device memory 331 and may be updated on a regular basis inconnection with receipt of updated neighbor cell lists from the servingbase station 204. As a result, the wireless device processor 329 may mapthe identifier of the base station 203, 205 that transmitted thesubframe to the stored information mapping identifiers associated withbase stations to positioning of resource elements and/or OFDM symbolscarrying positioning reference signals to determine the location and/orcharacteristics (e.g., duration and/or cyclic prefix) of such resourceelements and/or OFDM symbols within a particular received subframe.

After the wireless processor 329 has determined the sets of resourceelements in which the positioning reference signals were transmitted inthe subframes received from the base stations 203, 205 based onidentifiers associated with the base stations 203, 205, the wirelessdevice processor 329 processes the sets of resource elements to estimatetimes of arrival of the respective positioning reference signals basedon a local oscillator frequency of the wireless device's localoscillator 332. The wireless device processor 329 then provides theestimated times of arrival in an message (e.g., in a radio resourcecontrol measurement report message transmitted by the wireless device201 on the uplink) to the wireless device transmitter 325 fortransmission to the serving base station 204 and ultimatelycommunication to the location server 207 for determination of thewireless device's location. Alternatively, as discussed above, when thewireless device processor 329 has been programmed to autonomouslyestimate the wireless device's location, the wireless device processor329 may compute its own location based on the estimated times of arrivaland other information as may be provided to the wireless device 201and/or stored in the wireless device memory 331 (e.g., base stationlocations, transmission times of the subframes, channel conditions, andso forth as is known in the art).

The instructions illustrated in FIG. 7 for controlling operation of thebase station processor 316 (e.g., 401-413) logic flow blocks may beimplemented as programming instructions, which are stored in basestation memory 318 and executed at appropriate times by the base stationprocessor 316. Similarly, the instructions illustrated in FIG. 8 forcontrolling operation of the wireless device processor 329 (e.g., logicflow blocks 805-815) may be implemented as programming instructions,which are stored in wireless device memory 331 and executed atappropriate times by the wireless device processor 329.

As detailed above, embodiments of the present disclosure resideprimarily in combinations of method steps and apparatus componentsrelated to communicating positioning reference signals to aid indetermining a geographic location of a wireless communication device.Accordingly, the apparatus components and method steps have beenrepresented, where appropriate, by conventional symbols in the drawings,showing only those specific details that are pertinent to understandingthe embodiments of the present invention so as not to obscure thedisclosure with details that will be readily apparent to those ofordinary skill in the art having the benefit of the description herein.

In this disclosure, relational terms such as “first” and “second,” “top”and “bottom,” and the like may be used solely to distinguish one entityor action from another entity or action without necessarily requiring orimplying any actual such relationship or order between such entities oractions. The terms “comprises,” “comprising,” and any other variationsthereof are intended to cover a non-exclusive inclusion, such that aprocess, method, article, or apparatus that comprises a list of elementsdoes not include only those elements but may include other elements notexpressly listed or inherent to such process, method, article, orapparatus. The term “plurality of” as used in connection with any objector action means two or more of such object or action. A claim elementproceeded by the article “a” or “an” does not, without more constraints,preclude the existence of additional identical elements in the process,method, article, or apparatus that includes the element.

It will be appreciated that embodiments of the base station 301 and thewireless communication device 201 described herein may be comprised ofone or more conventional processors and unique stored programinstructions that control the processor(s) to implement, in conjunctionwith certain non-processor circuits, some, most, or all of the functionsof the base station 301 and the wireless communication device 201 andtheir operational methods as described herein. The non-processorcircuits may include, but are not limited to, the transmitters 312, 325,the receivers 314, 327, the antennas 304-307, 39-310, 320, 322-323, thelocal oscillator 332, the display 333, the user interface 335, memory318, 331, and the alerting mechanism 337 described above, as well asfilters, signal drivers, clock circuits, power source circuits, userinput devices, and various other non-processor circuits. As such, thefunctions of these non-processor circuits may be interpreted as steps ofa method in accordance with one or more embodiments of the presentinvention. Alternatively, some or all functions could be implemented bya state machine that has no stored program instructions, or in one ormore application specific integrated circuits (ASICs), in which eachfunction or some combinations of certain of the functions areimplemented as custom logic. Of course, a combination of the twoapproaches could be used. Thus, methods and means for these functionshave been generally described herein. Further, it is expected that oneof ordinary skill, notwithstanding possibly significant effort and manydesign choices motivated by, for example, available time, currenttechnology, and economic considerations, when guided by the concepts andprinciples disclosed herein will be readily capable of generating suchsoftware instructions or programs and integrated circuits without undueexperimentation.

While the present disclosure and the best modes thereof have beendescribed in a manner establishing possession and enabling those ofordinary skill to make and use the same, it will be understood andappreciated that there are equivalents to the exemplary embodimentsdisclosed herein and that modifications and variations may be madethereto without departing from the scope and spirit of the inventions,which are to be limited not by the exemplary embodiments but by theappended claims.

What is claimed is:
 1. A method in a wireless terminal, the methodcomprising: identifying a positioning subframe that may contain apositioning reference signal (“PRS”) transmitted by a first base stationbased on information signaled from a serving base station, thepositioning subframe comprising OFDM symbols over which a transmissioncorresponds to resource elements arranged on a subcarrier-OFDM symbolgrid; determining whether the identified positioning subframe containsresource elements corresponding to the positioning reference signalbased on information signaled from the serving base station; receivingthe identified positioning subframe; estimating a time of arrival of thereceived positioning subframe based on the PRS contained in the receivedpositioning subframe; and receiving the positioning reference signal ona first set of OFDM symbols where the positioning reference signalresource elements are obtained by taking Fast-Fourier Transform of atime-domain sequence obtained from a pseudo-random sequence generator;wherein initialization of the pseudo-random number generator isdetermined from any one of: a site identifier of the serving basestation, a physical cell identity of the serving base station, a globalcell identity of the serving base station, a system frame number, asubframe number, a resource element block index, a radio networktransaction identity, and information signaled by the serving basestation.
 2. The method of claim 1 further comprising: estimating a timeof arrival of the transmission from the first base station relative to areference dock based on the positioning reference signal; estimating atime of arrival of a transmission from a second base station; computinga time difference of arrival of the transmission from the first basestation relative to the transmission from the second base station; andsending a measurement report to the second base station including atleast the time-difference of arrival and an identifier associated withthe first base station.